The present invention relates to catalytic reforming using platinum-rhenium catalysts with relatively high rhenium content.
Catalytic reforming to upgrade naphtha or low-boiling range hydrocarbons to higher octane gasoline has been practiced for many years using catalysts comprising platinum on a refractory support, such as alumina. In the 1960's a major advance was made in this area when it was discovered that, in reforming a low-sulfur content hydrocarbon feedstock, the use of a catalyst comprising platinum and rhenium on alumina provided greatly improved yield stability and a much lower fouling rate. See U.S. Pat. No. 3,415,737 to Kluksdahl.
Since that time, a number of other patents have issued in the area of catalytic reforming using platinum rhenium catalysts. Some of these patents have been particularly focused on use of relatively high rhenium to platinum ratio catalysts, including the following: U.S. Pat. No. 4,356,081 to Gallagher, which discloses the use of catalysts having rhenium to platinum ratios of from about 1.08 up to as high as 17, rhenium contents from 0.362 to 0.875 weight percent and platinum contents from 0.05 to 0.344 weight percent; U.S. Pat. No. 4,425,222 to Swan, which discloses multi-stage reforming using forward reactors having a catalyst with rhenium to platinum ratio less than 1.2, a rearward reactor having a catalyst with a rhenium to platinum ratio greater than 1.5, and a swing reactor having some catalyst of each ratio; U.S. Pat. No. 4,427,533 to Swan, which discloses forward reactors having a rhenium to platinum ratio of less than 0.5, intermediate reactors having a rhenium to platinum ratio of less than 1.2 and a rearward reactor having a rhenium to platinum ratio greater than 1.5; U.S. Pat. No. 4,436,612 to Oyekan et al, which discloses the use of catalyst in forward reactors having a rhenium to platinum ratio of less than 1.0 and rearward reactors containing catalyst with rhenium to platinum ratio greater than 1.5; U.S. Pat. No. 4,440,626 to Winter et al, which discloses forward reactors having a rhenium to platinum ratio of less than 1.2 and rearward reactors (which contain 40 to 90% of the catalyst) having rhenium to platinum ratio greater than 1.5; U.S. Pat. No. 4,440,627 to Markley, which discloses catalytic reforming with forward reactors having a catalyst with rhenium to platinum ratio less than 1.2 and rearward reactors having a catalyst with rhenium to platinum ratio greater than 1.5 and with the start of run temperature being between 875.degree. and 930.degree. F.; U.S. Pat. No. 4,440,628 to Winter et al, which discloses reforming with the catalyst in the rearward reactor havihg a rhenium to platinum ratio greater than 1.5 and with certain process limitations; U.S. Pat. No. 4,464,249 to Mooi, which discloses reforming using a catalyst with rhenium to platinum ratios from 0.5 to 3.4 and with the platinum content of the catalyst in the first reforming stage being from 1.5 to 10.0 times the amount of platinum in the last stage; U.S. Pat. No. 4,613,423 to Swan which discloses staged reforming using a catalyst containing platinum-rhenium-iridium; and U.S. Pat. No. 4,613,424 to Schorfheide which discloses addition of sulfur to a rearward reactor in a multi-stage reforming process which uses platinum-rhenium or platinum-rhenium-iridium catalyst.
The references referred to above are not directed to the use of catalytic reforming catalysts containing rhenium in excess of a base ratio of rhenium to platinum. Also, the references do not direct toward the use of high rhenium to platinum ratio catalyst in the first stage (although the language may admit of such use in some instances) and instead, the references tend to direct away from the use of high rhenium to platinum ratio catalyst in the first stages. See, for example, the Mooi reference which states at Column 2, line 38,
"It has been found that the presence of rhenium tends to inhibit and have a deleterious affect upon the activity of the platinum group metal catalyst to catalyze a naphthene dehydrogenation reaction."
Naphthene dehydrogenation is one of the main reactions taking place in the first stage of a multi-stage catalytic reforming unit. Also, it may be noted that typically in the above references, the ratios of rhenium to platinum preferred for the first stage catalysts are 1.2, 1.0, or lower ratios.